Support configurable property file encoding

[pbarnes-tibco]

The read-project-properties, write-project-properties, and write-active-profile-properties goals read/write from properties files using java.util.Properties default encoding, ISO 8859-1. It would be useful to be able to specify the encoding to use when reading or writing the property files. I have a use case where a properties file encoded in UTF-8 contains some characters which are not mappable to ISO 8859-1.